Detection of Bioaerosols Using Multiwavelength UV Fluorescence Spectroscopy

Abstract

This article describes the development of an aerosol generation apparatus to investigate the fluorescence spectra of bioaerosols. The experimental system was set up in a Biosafety Level II Laboratory. The system included an aerosol generator, chamber, aerosol monitoring instrumentation, and laser-induced-fluorescence detection system. The aerosol generators, chamber, and monitors were housed in an enclosure with the exhaust vented through a double HEPA filtration system. A Hospitak nebulizer using aqueous suspensions generated aerosols of bacteria. Aerosols of pollens were generated using a small-scale dry powder generator. The aerosol chamber, with four windows for optical access, was designed with the aid of a computational fluid dynamics code to optimize the generation of aerosol beams with a well-defined geometry for reproducible fluorescence measurements. Aerosol concentrations and aerodynamic diameters in the chamber were determined using a filter, an impinger, a modified Andersen impactor, and an Aerodynamic Particle Sizer. Geometric size and particle shapes were determined using microscopy and imaging analysis. The well-characterized aerosol stream allowed reproducible fluorescence measurements to be made with the aerosol generation methods developed in this work. Fluorescence spectra of four bacteria, Escherichia coli, Staphylococcus aureus , Bacillus subtilis var niger , and Bacillus thuringiensis , were found to be very similar. Calibrations of the fluorescence instrumentation allowed cross sections of live cells, killed cells, and spores to be measured with an uncertainty of about 2 to 5.